An internal combustion engine (hereinafter abbreviated as “engine”) of an automobile or the like is configured such that a combustible mixed gas is formed by mixing fuel injected from a fuel injection device and air introduced into the engine through an intake pipe, and the combustible mixed gas is burned in the inside of the cylinder. It has been known that, in such an engine, a mixing state of the fuel injected from the fuel injection device and the air largely influences the performance of the engine. Particularly, it has been known that the atomization of the fuel injected from the fuel injection device becomes an important factor, which influences the performance of the engine.
Such a fuel injection device, in order to ensure the atomization of the fuel in spraying, is configured such that a nozzle plate is mounted on a fuel injection port of a valve body to inject the fuel from a plurality of fine nozzle holes formed on this nozzle plate.
FIG. 16 shows such a conventional nozzle plate 100. This nozzle plate 100 shown in FIG. 16 has a laminated structure formed such that a first nozzle plate 101 and a second nozzle plate 102 are laminated. Then, as shown in FIG. 16 and FIG. 17, at the first nozzle plate 101, a pair of first nozzle holes 103A and 103B, which pass through front and rear surfaces of the first nozzle plate 101, are formed at positions on a center line 104, which extends along a Y-axis, and positions that are mutually line-symmetric with respect to a center line 105, which extends along an X-axis. As shown in FIG. 16 and FIG. 18, at the second nozzle plate 102, a pair of second nozzle holes 106A and 106B are formed at positions on the center line 105, which extends along an X-axis direction, and positions that are mutually line-symmetric with respect to the center line 104, which extends along the Y-axis. These pair of second nozzle holes 106A and 106B are communicated with the first nozzle holes 103A and 103B via a pair of curving channels 108A and 108B (a first curving channel 108A and a second curving channel 108B) formed at a side of a surface (front surface) 107 bumped against the first nozzle plate 101. At the second nozzle plate 102, the pair of curving channels 108A and 108B are communicated with one another by a communication channel 110, which extends along the center line 104.
The conventional nozzle plate 100 shown in FIG. 16 guides the fuel injected from the fuel injection port of the valve body into the curving channels 108A and 108B from the first nozzle holes 103A and 103B, and while performing a swirling movement to the fuel flowed into the curving channels 108A and 108B by the curving channels 108A and 108B, flows the fuel outside from the second nozzle holes 106A and 106B to ensure improvement of a quality of the fuel atomization (see Japanese Unexamined Patent Application Publication No. 10-507240).
However, as shown in FIG. 16 and FIG. 18, in the conventional nozzle plate 100, the second nozzle holes 106A, 106B of the second nozzle plate 102 are shaped in a round hole having the same inner diameter consistently from a fuel inflow end (an opening end on the first nozzle plate 101 side) to a fuel outflow end (an opening end on the side of an outer surface of the second nozzle plate 102), in which the fuel outflow end is a sharp edge orthogonal to the outer surface of the second nozzle plate 102. Therefore, the fuel particle in spraying is insufficiently atomized and homogeneous.
Therefore, an object of the present invention is to provide a nozzle plate that can sufficiently spreads the spray generated by injection of fuel from a nozzle hole, ensures further minute fuel microparticles in spraying, and ensures the further homogeneous fuel microparticles in spraying.